Part of the demographic issue is caused by economics. It costs thousands of dollars to have a baby who has zero problems. It costs thousands more to raise that child to adulthood. People are having fewer children so they can invest more in the ones they have. This is what happens to every developed economy. This is why socialist countries have an even worse demographic issue. Socialism distributes poverty and poverty means people will have fewer children, because, by whatever means, having a child is a choice.
Improve the economy so that average people feel well off and the problem of fewer children will resolve itself. Tax the heck out of them, and they will have fewer children.
You lost me at “poverty means people will have fewer children”.
How do you explain India? American ghettos? Central and South America?
Generally, the more prosperous the country, the lower the birthrate. There are many reasons for it, but the idea that a country must have an ever increasing population to have a viable economy, just doesn't comport with the facts.